Laboratory equipment used for distillation of essential oils is called Clevenger type apparatus as shown in FIG. 1 of the drawings accompanying this specification. Reference may be made to Clevenger type, J.F., Apparatus for the determination of volatile oil. J. Amer. Pharm. Assoc., 17, pp. 346(1928), wherein the apparatus (1) is attached to the spherical glass vessel (a) having charged with the plant material along with water in 1:2 ratio through opening (b) which is also used for discharging the mixture after process is complete. The whole system is put on a heating mantle (c), which has an energy regulator (d) for controlling the temperature. After few minutes, the material inside starts boiling. The vapors so formed are passed through a vertical condenser (e) through a long vertical glass tube (f). The cold water around the condenser tube is circulated through inlet (g) and outlet (h). The condensed distillate gets collected in a measuring tube (i) connected to the outlet of the condenser where an air outlet (j) open to atmosphere is placed. The volatile oil separates as an upper layer, from the distillate because of its density difference, as the oil is lighter than the water. A return tube (k), for recycling of aqueous part of the distillate, connects the bottom of the measuring tube (i) and vertical tube (f). The oil is collected at the outlet by opening the stop-cock valve (l).
The major drawback of the apparatus is that it was designed to distillate the plant material by water distillation at normal atmospheric pressure only. There are some aromatic plant materials exclusively distilled by steam distillation method rather than water distillation, reason being that some of volatile constituents get hydrolyzed due to the presence of excessive water in the vessel. The apparatus works neither on the principle of steam distillation nor on water and steam distillation technique. Clevenger type apparatus is generally restricted to laboratories for the essential oil estimation but cannot be used to produce the essential oil in higher quantities. Since the system is heated up with the help of electric mantle (c) only, with very small batch capacity of material charging vessel (a), long vertical glass tube (f) and condenser (e) are made up of glass which requires careful handling and can not be heated without electricity which is difficult for a marginal farmer with small land holdings in remote areas. The recovery and quality of the essential oil distilled in this glass Clevenger type apparatus is of inferior quality. The color of the oil is generally lighter than the commercially distilled oil, which is not recommended in the market. Pure distillation is not possible since the oil is obtained with other materials/contaminants.
There are distillation units, which are operated by Water and Steam distillation method. Water and Steam distillation method involves a distillation tank with a false bottom and with or without Calendria at the bottom. Cohobation column at the top which is connected to the condenser and a distillate receiver. The plant material is charged from the charging hole and closed tightly. Prior to charging of plant material some fresh water is added to the tank and the precautions are to be taken to control the water level which should not touch the false bottom. The water level is maintained by recycling the distillate collected in the receiver to the tank or continuous or batch-wise fresh water is supplied to the tank. The tank is heated by direct firing of the agro-waste from the hearth bellow. The purpose of this method is to reduce the effect of hydrolysis of essential oil which are get hydrolyzed when they came in to continuous contact with excess water. After few minutes the water vapors starts forming and extracts the essential oil from the plant material and carries it over to condenser where they are condensed to liquid distillate. The distillate is collected in a receiver where it is separated in to two fractions; one as an essential oil and other as saturated water layer. The essential oil is separated, cleaned and then stored as per the recommended methods.
The major drawbacks of the unit are that it can not distill the plant material by Steam distillation. Some parts of the aromatic herbs such as cedar wood, sandalwood are preferably distilled by Steam distillation method to obtain better recoveries and quality. Also these units can not distill the plant material neither at reduced pressure nor at higher pressure since the system is opened to the atmospheric pressure and can not operated as a closed system. Being an industrial size, these units can not be a portable systems and thus difficult to take them to the fields where the plant material is available in remote areas and distilling the fresh raw material is not possible in such a system which is one of the major parameter in affecting the quality of an essential oil. Being commercial scale units they requires more man power, operational costs etc., and the marginal farmers can not afford to purchase these industrial scale distillation units.
The widely used hydro distillation method in the essential oil industry is Steam distillation
The units used to perform the Steam distillation method merely consists of a distillation tank with a false bottom fixed at a certain height from the bottom of the tank. A spurger is provided below the false bottom, which is connected to the industrial size boilers. The plant material is placed above the false bottom and then the lid is closed tightly by nut-bolts. Steam generated from the boiler is fed to the tank through the fixed steam spurger to commence the distillation. After few minutes the vapors starts forming which are taken to the vapor inlet of a shell and tube condenser, which is connected to the vapor out, let of the distillation tank at the top. The condensed liquid is collected in a receiver where the essential oil and distillate are separated.
The major drawbacks of the unit are that it cannot distill the plant material neither by Water distillation nor by Water and Steam distillation. Some parts of the aromatic herbs are preferably distill by Water distillation method to obtain better recoveries and quality. Also these units can not distill the plant material neither at reduced pressure nor at higher pressure since the system is opened to the atmospheric pressure and can not operated as a closed system. Being an industrial size these units cannot be a portable, and thus difficult to take them to the fields where the plant material is available in remote areas and distilling the fresh raw material is not possible in such a system which is one of the major parameter in affecting the consistency in the quality of an essential oil. Being commercial scale units they require more man power, operational costs etc., and the marginal farmer cannot afford to purchase these industrial scale distillation units.
Thus, apparatus, industrial scale units and the process mentioned above has one or the other major drawbacks like inferior oil quality, low oil recovery, low batch capacity, lack of water distillation, steam distillation and water and steam distillation facility, restricted mode of heating, unable to distill the plant material under vacuum and at higher pressures, difficulty in charging and discharging of plant materials because of narrow mouth and requires more attention during processing, more capital investment, operational cost.